When hard disc drives are used in laptop, desktop and server applications, the hard disc drive is enclosed in a computer housing. The thermal mass of the housing tends to buffer or slow down a rate of temperature drop in the disc drive when the surrounding environment cools. With these slower temperature drops, there is usually enough time for humidity in the disc drive to slowly vent into the surrounding environment through a filter so that condensation inside the disc drive is avoided. However, as smaller disc drives are increasingly used in portable devices such as MP3 music players and personal digital assistants (PDAs) which have low thermal mass, there are more rapid temperature drops in the disc drive and condensation inside the disc drive can occur. In particular, a disc drive may be carried from a warm humid indoor environment to a cold outdoor environment and condensation will form in the disc drive as the disc rapidly cools.
When condensation forms inside the disc drive, it can adversely affect disc write operations because moisture on the magnetic disc surface is known to adversely affect disc lubrication and head-media spacing. The condensation can cause head crashes. Condensation on the disc also causes an effective change in the coercivity of the media and will generally create bad writes and media defects.
The problem with condensation is particularly difficult in hard disc drives and other enclosed assemblies which are completely sealed except for a filter which keeps contaminating particles out of the enclosed assembly but permits pressure equalization. There is little exchange of air between an interior space of the disc drive and its surrounding environment, except during temperature changes. Changes in environment temperature can draw humid air into the disc drive, and then it is difficult to remove the humidity.
A method and apparatus are needed to prevent damage to moving parts in an enclosed assembly when moisture condensing conditions are present inside the enclosed assembly. Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.